The present invention relates to reusable anchors to support instruments such as drills. More particularly, the present invention relates to variably eccentric anchors which may be entirely removed from the substrate upon completion of the drilling process.
A variety of different types of locking connectors have been proposed in the prior art. Where the substrate is a relatively hard material, such as concrete, anchor holes are formed in the substrate in order to provide a seat to receive an anchor for securely holding in place drill frames or other instruments to be used.
The most common fasteners for securing the instruments in the anchor hols are anchors that remain in the substrate after the instrument have been disconnected. Such expandable anchors may be inserted into the substrate when the substrate is still in a moldable form, as in the case of wet concrete, or may be inserted into the substrate when the substrate has hardened. The anchors are typically left in the substrate after they have served their fastening function, though they may be removed after use, with varying degrees of difficulty. If removed, the anchors may need to be reformed prior to repeat usage. The costs associated with inserting and removing such anchors, as well as the cost of the anchors themselves, may be substantial where the project in question requires a large number of such anchors.
U.S. Pat. No. 2,691,293 illustrates one contemporary anchor with a curved lower end which is intended to be embedded in place in the concrete when poured. The anchor provides an exposed portion which is threaded for attachment of the devices to be anchored. However, the anchor is not removeable or reusable.
Other contemporary anchors are not embedded in the concrete when poured, but rather later inserted into predrilled holes. The deterioration of the concrete surrounding the holes, however, causes substantial difficulties in maintaining a tight fit between the anchor and the concrete, sometimes causing the anchor to fail. Where the hole is exposed to water penetration, the effects of freezing and thawing often cause deterioration or crumbling of the surrounding concrete which detracts from the ability of anchors to hold the concrete. Moreover, such anchors, if left in the substrate, will often rust with rain and result in undesirable rust lines bleeding from the anchor along the surface of the substrate.
In addition to damage from water or other external factors, the normal slow crumbling of the concrete may allow the anchor to rotate in the hole and ultimately result in failure of the anchor. Though some devices, such as that disclosed in U.S. Pat. No. 4,250,681 disclose techniques for maintaining an anchor within a preformed slot, such devices require the use of additional plugs placed in abuttment with the anchor to maintain the anchor in place and require the drilling of angled holes in the concrete to receive the anchor.
From the foregoing, it can be seen that it is desirable to have a removeable anchor that may be readily placed into an anchor hole and adjusted to grip the hole firmly without the need for additional cooperating elements, and may be readily extracted from the hole upon completion of the drilling steps.